Antithesis
by MinorCutie
Summary: Submission for Starco Week 3: Day 1! Bad Boy x Princess AU - Locked in a mysterious tower, our two favorites find themselves with completely different personalities! With no way out but to work together, will they be able to find a way to switch back?


**Thank you for all of the positive feedback I received on my last story!**

 **I've decided to take part in Starco Week 3 on Tumblr, so here's the prompt for Day 1.**

 **"** **Monday, April 3rd:** _ **Bad Boy x Princess AU -**_ **Total opposites of how they appear and act in the show, so how well do they maintain this wild relationship of theirs?"**

* * *

Marco couldn't be for certain, but he estimated that it had been about four hours since his feet had touched dry land. In the middle of an unknown Mewni river, Star sat atop a perch at the head of their boat.

"How much longer, Sta-a-ar?" Marco groaned, dragging out the middle of her name.

"We're almost there. I can feel it!"

If Star was being honest with herself, however, she _was_ a little lost. She had followed the directions perfectly, and yet no ghostly ruins had come into sight. Not much would be lost if they abandoned ship now. There wasn't any specific reason she needed one of the artifacts from the ruins, she just thought it was pretty. She had expertly hidden that little detail from Marco, though.

The duo was just about to call it quits when out of the corner of Marco's eye, a large structure peaked out from above the treeline.

"Can that please be what we're looking for?" He pleaded and pointed towards the tower.

"Actually, it might be!"

It wasn't a long walk to the ruins, but Marco's shaky legs and post-motion sickness nausea made it hard to keep up with his bouncing, bubbly friend. Star had long reached the inside of the crumbling building they were looking for when Marco finally trudged up the steps.

The inside of the tower was gloomy and dim, the only light coming from the small doorway and tiny windows at the peak. The round room appeared to be about three times the size it looked like from the outside. From the floor to as far as they could see into the pitch-blackness of the ceiling, deep inscriptions covered the wall's surface.

"I can't seem to translate what the wall is saying. Some parts are missing, but look at this weird hand-thingy!"

A small, square pedestal was protruding from the middle of the floor. Besides the unreadable text being scrawled across the top surface, a pair of hand prints were embedded into the stone. The prints were huge in comparison to the small fist of a princess.

Star, of course, slapped her hand down anyway, "I wonder what this does!"

"Maybe it's just like a signature from whoever wrote all this...stuff." Marco peeked under the pedestal and found more letters, but this time they were a little more haphazardly written.

"Nope! I read that you have to pass a puzzle to get to the secret prize," She did a slow twirl to glance at the rubble around her. "This is the only building still standing, so we have to figure out how to get to the top."

"That's a long way up for a couple of kids with no stairs. How're we gonna make it?"

"Magic, duh."

"Of course," He chuckled to himself.

Star again had her small palm placed against the print and Marco couldn't help but notice how it seemed to swallow her tiny hand up. Curious to how his own would look against it, he filled the right side of the impression.

Suddenly, thousands of the foreign letters on the wall lit up around them. Star and Marco were unable to lift their hands from the surface now as if someone was holding them in place.

Marco panicked and grabbed the wrist of his stuck arm, firmly tugging away, "Star, what do we do?"

"I don't know! I'm frozen solid"

She was right, as much as he struggled, Marco couldn't even continue pulling now. The duo was as still as statues, paralyzed from the neck down and terrified. The lit up letters, however, danced around the room now, circling around as if to flaunt their ability to move.

"Can you use your wan-" Marco began to shout, but it was too late. The bright light from the inscriptions had filled the room with a blinding intensity and completely enveloped the two teenagers.

From head to toe, they glittered brightly and could both feel a slight tingling sensation. It wasn't painful, but definitely uncomfortable when paired with the inability to move.

When the chaos stopped, they found themselves in complete darkness.

Marco was the first to stir and he rubbed his throbbing forehead.

 _At least I can move now._ He sighed with relief. _And I'm alive._

"Hey, princess," He lightly kicked the slumped form next to him. His eyes were now adjusting to the dark, but she was about all he could see. "You dead?"

"Ow! Please don't kick me." She mumbled, rubbing the afflicted arm. "I can't see you."

"How about using that wand you love _correctly_ for once?" Marco huffed, crossing his arms.

"O-oh, right," Star stuttered. Within a few seconds, a soft pink glow radiated from the wand. It didn't entirely fill the room, but it was enough to show that the walls around them were now completely blank. All of the writing that had just been circulating around them was gone and replaced by normal, smooth stone.

Marco stood, grunting as his joints popped from standing straight. While looking around the room, he didn't notice a tiny outstretched hand until Star had cleared her throat for the third time.

"What?" He asked bluntly. The boy's arms never moved from their place on his hips and he barely tilted his head towards her crumpled body.

"Are you not going to help me to my feet?" Star's eyes blinked rapidly in confusion. Her open palm was still eagerly reaching towards him.

"Are your legs broken or something? Help yourself up." A quick turn on his heel spun him away from the princess and closer to the pedestal that somehow remained standing. Its surface was also blank and smooth, however, devoid of any proof the hand prints existed.

Star's jaw dropped, as did her arm, finally. When she reached her feet, she delicately brushed off her dress and combed her long fingers through blonde hair.

"I do not appreciate your tone, you know," She began. "It's very rude of you to not help a princess, in any case."

Her speech continued on, but Marco barely noticed. He was too busy feeling the wall around him, searching for any sign of the doorway they came through. Her soft, but determined, voice was like nails grating against a chalkboard to him. He had made a full rotation of the room and tried his dimensional scissors, but Star had not stopped but to take a breath in between sentences.

"And another thing, -" She grumbled,

Marco finally broke and shouted to mock her, "And another thing! We wouldn't be in this mess if it wasn't for your stupid idea anyway! I bet you don't even know what that artifact _looks_ like."

She shriveled under his hateful gaze, "I thought perhaps I would know it when I laid my eyes upon it."

"I knew it!" He shouted, throwing his arms up into the air. "And stop talking like that, you sound ridiculous."

Star suddenly grabbed her forehead, wincing and leaning forward in pain.

"What's happening to us, Marco?"

Marco doubled over in agony as well, stammering, "I don't know! I just -"

With their heavy breathing matched, the duo looked into each other's eyes and whispered, _"What's going on?"_

Another hour of their arguing had continued before they noticed the strange markings on their palms. On the hand they used to touch the pedestal, a small phrase had been almost tattooed onto their skin.

 ** _\- It all begins and ends with your antithesis -_**

"What the hell does that even mean?" Marco scoffed.

"Maybe we should just continue our journey to the top?" Star questioned, looking up to the small squares of light from above. It seemed like the building continued on forever, but there was definitely an end. As the day went on and the direction of the light changed, Star could now see a platform jutting out from the side of the wall.

"Don't you have that weird cloud thing that can just take us to the top?" Marco was leaning against the wall now, mindlessly picking at his hoodie string.

"You are correct," The princess replied, "But I'm not sure I have the energy to do that right now. Could I take a nap first?"

"You have got to be kidding me," Rolling his eyes, Marco threw his head back against the wall, but instead of his skull smacking against the stone, a small brick-sized piece of rubble was pushed inward.

"What the..."

A faint rumble shook the floor beneath them. For a few moments, nothing happened, but then a large piece of stone erupted from the wall, almost knocking Marco to the ground. Several more blocks appeared, each one rising a bit higher than the other to spiral up the building. They could only hope that the stairs continued on to the platform, and there was only one way to find out.

"Alright, Princess. Time to climb." Marco grunted and placed a foot on the first step. With his hands in his hoodie pockets, he turned to Star after she didn't budge from her place by the pedestal.

"Carry me, please. I've already told you how exhausted I am, I'm feeling as if I might faint." She replied, not quite a whisper with her sugary sweet tone.

His arms flew from his pockets and out towards Star, palms up. "No way!"

"Then I suppose you'll have to wait until after my nap. Lend me your clothes."

"Excuse me?" Marco's patience was wearing thin.

"What? Do you think I'm just going to lay on the _ground?_ Like a savage?" Star crossed her arms over her chest. Her eyebrows were raised with such intensity that little wrinkles formed on her forehead.

"I don't think you have much of a choice."

"I don't, but _you_ do. Carry me on your back and I won't have to sleep at all."

"No! I would rather throw myself off these stairs than carry you." Marco replied, both literally and figuratively putting his foot down.

But he should have known better than to argue with a sleepy princess.

* * *

Marco had just about reached the first platform when Star's left boot began to wriggle off her toes.

"I'm slipping," She whined. "Can't you readjust me?"

"We're here. Now get off."

Star was non-ceremoniously dumped from Marco's back with a loud _thud_ which fixed her shoe back into place quite well. Pleased with how gracefully she landed despite the circumstances, a large smile crept onto her face.

"Don't look so happy just yet." Marco pointed to a figure short in stature, with rounded horns poking out the side of her skull.

The demon was peacefully sitting crisscrossed against the wall, eyes closed and fingers bending in a shape no human could recreate.

"Welcome!" Her soprano voice echoed around them. "I am Lily! I've visited you because it seems you have an issue and need to get to the top of this tower."

Star bowed politely, "Nice to meet you, Lily. I'm Star and this is -"

"Don't tell her my name, you idiot! Never tell a demon your name," Marco raged. "And _you're_ the one from the magical world. Jesus Christ."

He turned to the demon girl now, with an eyebrow raised, "An issue? What do you mean by that?"

"Well, besides the fact that the door to the tower sealed on you, isn't it obvious?" She looked between Marco and Star, gesturing to the both of them. "Do you not feel different?"

"I feel that you're in my way." He scowled.

"My head hurts!" Star chimed in, rubbing a particular spot on her hair line.

"One out of two isn't bad, I guess. Let's just get on to our first test!" Lily smiled, but after a long, silent pause, you could feel her nervous energy emanate through the room.

Her eyes had yet to open, but her fingers nervously twitched every now and then, each passing form becoming more and more difficult to copy.

"I think you'll find that me being Mewni royalty alone will be enough to pass the test. I am the next in line for the thrown, after all." Star nodded confidently, smiling a big, toothy grin.

"Actually, Princess," Lily's eyes finally opened, they blazed intently with what seemed like every shade of blue at once. "I think you'll discover that your confession will make your test only that much harder."

The first assuring sentence from her seemed a little forced to Marco. He watched how she shifted nervously when the demon thought neither of them was watching. Something wasn't completely right here, and maybe he could find a way to get past her. Test or no test.

"Go sit on the steps, Star." He motioned behind him without looking her in the eyes.

"I think I can be of help, though!"

"You will literally just get in the way," He pointed again towards the steps as if signally to a dog. "Go."

The throbbing twinge in his temple didn't go unnoticed, but he held back with everything he had to not double over. He wanted this conversation to go as smoothly as possible and that wouldn't be too good of a start.

"So, Lily," Marco began. "About this test."

"You approach me so casually, mortal. You'll find out what the test is soon, it's j-just not ready yet." Her one stumble gave Marco the exact opening he was looking for.

"Is this your whole job or whatever? Making unsuspecting people answer questions they probably don't know the answer to?"

Her face was blank, unblinking.

"Or let me guess," He crouched down to her height, placing an open palm on the wall to the side of her head. "Is this your first time? You have no idea what you're doing, do you?"

He spoke in a tone so low, so embarrassingly deep, that a bright-fuchsia blush began to creep over her cheeks from his question.

"H-how did you know! I didn't even b-begin!" She stuttered, her little horns glowing red in the darkness.

Her expression turned to one of pure bewilderment. "I c-changed my mind! I'm not doing the test now. You'll just get to sit here forever!"

"Is that really what you want? Because I can sit here for a couple more hours and make you feel like shit, easy."

"Hmpf!" She crossed her arms over her chest, "I can't even stand to look at your face right now!"

"Same." Marco's reply was completely monotone.

"Fine! Just get out of here!"

He chuckled and stood tall above the demon girl. "Well, that was easy enough. Let's go, Star."

The princess dusted off her dress before prancing over to where the stairs were materializing from the wall.

"Oh, I do hope she'll be alright," Star whispered to Marco. "You've embarrassed her to death."

"She'll get over it," Marco replied, not even bothering to lower his voice.

"You'll never escape!" Lily shouted from behind, but the two of them were already several steps toward their destination.

The tower grew brighter around them as they reached the second platform. Upon closer inspection, Star noticed that the windows of light were covered in plant life and she stopped to marvel at their beauty.

Marco didn't notice until he was a couple of steps ahead. He was about to turn and bark an order at her to get moving, but that twinge in his temple stopped him in his tracks. As he looked down on Star from above and saw pure happiness spreading across her face, it almost took his breath away.

Why was he so _angry?_

His heart began pounding in his chest and when she finally turned to find him staring at her, Star blushed profusely, giving him a blinding smile. Her eye contact didn't last long, however, and her fingers wriggled around in front of her while she fidgeted. She was scared of him, and it was all his fault.

This brought Marco back to the present and his clear-headed thoughts ended almost as quickly as they came.

With a cough, he grunted, "Hurry up."

The princess followed the orders this time and quickly skipped past him.

She was the first to set foot on the top platform. While they were both expecting some horrible beast to be waiting and ready to fight, all they found was a single door. It was obviously aged as much as the rest of the tower, covered in the vines that crawled from the open rock windows. It appeared to be a typical door, with its only special characteristics being the engravings similar to what was written on the walls of the bottom floor.

"Is that it?" Marco questioned to the open room.

"Shall we try opening it?" Star questioned, taking a step towards it.

"Wait," A hand flew out in front of her body, stopping Star in her tracks. "It could be booby trapped."

The two pondered this for a moment before Marco said, "Star, give me your headband."

"What?" She shrieked, "Just what are you going to do to my accessory?"

In the blink of an eye, Marco pulled the horns from her head and tossed it towards the door. It slid across the stone before making a light _thump_ against the wood.

They waited, and waited, and waited for a possible attack, but nothing happened.

Star sighed in relief and picked her headband from the dirty floor, "I'm going to have mother send you to St. Olga's if you keep acting so rude."

What was supposed to be a simple turn of a knob turned into almost an hour of Marco trying to break it off with his kicks and Star shooting magic at it. Nothing affected the door, it didn't move a single centimeter, and so in the room, they stayed.

At one point they even tried to escape through the windows, but an invisible barrier had been placed to where they could see out but couldn't go through.

Frustrated to the point of tears, Star rested her head against the wood grain and sighed.

"Please?" She mumbled, "Please let us open this door."

A small _click_ echoed around the room.

"No!" Marco shouted. "You have _got_ to be kidding me. There's no way that could work."

But it did. The door opened with ease now and the two were able to walk out onto the balcony where the sun was just starting to set.

There, in the middle of the balcony, a pedestal rose from the stone. Almost identical to the one that had originally been on the bottom floor, hand-prints were engraved on the top. They both rushed to the pillar and slapped their respective hands in the slots, but nothing happened. No shining light, no flying letters.

The couple looked at their hands again.

"Antithesis," They both said out loud. "What could that mean?"

"Maybe if I -" Marco began, placing his opposite hand where Star's had been.

"And if I do this -" Star finished and did the same with his space.

Just as the sun was about to disappear over the horizon, their bodies lit up with a dazzling, yellow light. The tingling sensation returned, but this time it was welcomed. When the transformation was complete, the hand-prints were missing from the pedestal's surface again. This time, however, they were replaced with a glowing pink jewel surrounded by two small figures, hand in hand.

When the two regained consciousness, the sun had completely set and they found themselves in the darkness again.

"Just like the first time." Marco smiled, and Star made her wand light up around them.

"Yeah, 'cept this time you didn't kick me!" She giggled, but the corners of her eyes had already welled up with tears.

"Star, I'm so sorry!" He pulled her into a tight hug. "I don't know what just happened to us, but I was in there the whole time! Shouting for you! I'm so sorry!"

"It's okay. It's just...You were so _mean_ to me!" She replied, wiping her wet eyes off on his hoodie.

"And you were so proper. It was like you were a completely different person!"

"Wait," Marco looked down at his hands, but the mysterious tattoo phrase had disappeared. "Antithesis...I think whatever spell-thing that was in those hand-prints made us become our opposites."

Star nodded in response, "I'm just glad we're back now."

"Me too, I don't think that version of Star would have let me do this."

Marco placed a hand on either side of Star's head and gently smoothed his thumb over one of her cheek hearts. They smiled at each other before leaning in and touching their lips lightly against the others. It was the first kiss they had shared together, but it was long overdue.

"I needed to apologize somehow." He blushed.

Star placed her hands on top of his and smirked, "If this is how you say sorry, you should mess up more often!"

Now that they were out of the tower, Marco felt the familiar weight return to his dimensional scissors.

"Get your fancy tower prize, princess, and let's go home."

"Whatever you say, meanie-head!"

* * *

 **AN: I know it was pretty long for a Starco Week submission, but this might be the only day of the week I can submit so I wanted to make it count!**

 **I'd love to hear what you thought about it!**


End file.
